nir: Free liveness info when invalidating metadata

Liveness info can be huge, since with larger shaders it essentially
grows quadratically (linear increase in number of SSA defs *
linear increase in blocks).

Freeing liveness info early helps somewhat mitigate memory usage here.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29577>

src/compiler/nir/nir_metadata.c

@@ -66,6 +66,19 @@ nir_metadata_require(nir_function_impl *impl, nir_metadata required, ...)
 void
 nir_metadata_preserve(nir_function_impl *impl, nir_metadata preserved)
 {
+   /* If we discard valid liveness information, immediately free the
+    * liveness information for each block. For large shaders, it can
+    * consume a huge amount of memory, and it's usually not immediately
+    * needed after dirtying.
+    */
+   if ((impl->valid_metadata & ~preserved) & nir_metadata_live_defs) {
+      nir_foreach_block(block, impl) {
+         ralloc_free(block->live_in);
+         ralloc_free(block->live_out);
+         block->live_in = block->live_out = NULL;
+      }
+   }
+
    impl->valid_metadata &= preserved;
 }
 

src/compiler/nir/nir_sweep.c

@@ -47,15 +47,6 @@ sweep_block(nir_shader *nir, nir_block *block)
 {
    ralloc_steal(nir, block);
 
-   /* sweep_impl will mark all metadata invalid.  We can safely release all of
-    * this here.
-    */
-   ralloc_free(block->live_in);
-   block->live_in = NULL;
-
-   ralloc_free(block->live_out);
-   block->live_out = NULL;
-
    nir_foreach_instr(instr, block) {
       gc_mark_live(nir->gctx, instr);